This invention relates to a drafting unit for a spinning machine comprising several drivable bottom rollers, of which the feeding bottom roller is constructed as a sleeve which can be connected with a drive shaft by means of coupling devices.
In the case of a drafting unit of this type (German Patent Document DE 39 20 682 A1), a friction coupling is arranged between the sleeve and the drive shaft in the case of the feeding bottom roller, which friction coupling comprises two rings which are non-rotatably connected with the drive shaft, are arranged at a distance from one another and form friction areas with the opposite inner surfaces of the sleeve. Because of the draft between the feeding roller pair of the drafting unit and the roller pair which follows, the sliver to be drafted exercises a tensile force on the feeding bottom roller which results in a torque of the feeding bottom roller in the rotating direction of the drive shaft. An additional idle running device provides that this torque will not have the result that the sleeve rotates faster than the drive shaft. Because the sleeve is taken along by the sliver to be drafted, the take-along moment to be applied by the friction coupling only needs to reach a minimal value.
When the sleeve is stopped by means of a stopping element, for example, in the case of a yarn breakage, the drive shaft may continue to rotate while overcoming the frictional force of the friction coupling.
In the case of this known construction, there is the risk that the sleeve may rotate more slowly than the drive shaft which leads to faulty drafts in the drafting unit.
It is an object of the invention to develop a drafting unit of the initially mentioned type in such a manner that, while the drive shaft continues to rotate, the feeding bottom roller can be stopped individually, in which case a defined driving torque is ensured.
This object is achieved in that the coupling devices comprise a swivelling lever which can be applied radially to the drive shaft, engages in a catch of the drive shaft and whose swivel shaft is arranged on the sleeve.
In the case of this development, a form-locking coupling exists between the swivelling lever arranged on the sleeve and the drive shaft so that the sleeve rotates at exactly the same rotational speed as the drive shaft. After an uncoupling of the sleeve from its drive shaft by the disengagement of the swivelling lever from the catch of the drive shaft, the sleeve can be stopped individually although the drive shaft continues to rotate.
Advantageously, the swivel shaft is arranged in parallel to the axis of the drive shaft so that little space is required in the axial direction of the feeding. bottom roller for the swivel movement of the swivelling lever.
The swivelling lever is expediently arranged in the area of an end face of the sleeve. As a result, the coupling area can be separated constructionally from the bearing.
As a further development of the invention, a toothing is provided as a catch which is complementarily mounted on the swivelling lever as well as on the drive shaft. As a result, it is possible without difficulties to couple the stopped sleeve to the only slowly rotating drive shaft because a toothing ensures the play that is required for this purpose.
Advantageously, the toothing is provided on the drive shaft as an allround toothing. This accelerates the engaging operation because it is not necessary to wait until a catch moves by the area of the swivelling lever.
Advantageously, the axial course of the allround toothing corresponds to the width of the swivelling lever. This leads to a low constructional space requirement.
In an advantageous further development of the invention, the catch of the drive shaft is covered by the sleeve with the exception of the recess for the swivelling lever. As a result, the actual coupling part, apart from the swivelling lever that is visible from the outside, is situated in the interior of the sleeve so that any risk of injury is eliminated and any risk of contamination is minimized.
In a further development of the invention, the swivelling lever has two lever arms, of which one is assigned to the catch and the other is loaded by a spring in order to establish the coupling connection. This further development makes it possible to always press the swivelling lever against the catch of the drive shaft during the operation, in which case the springy devices can be mounted in the interior of the sleeve so that they are invisible from the outside.
It is advantageously provided that the moment of the spring which is effective with respect to the swivel shaft corresponds to the rotating direction of the drive shaft. In the case of such a development, the swivelling lever can be engaged in the catch of the drive shaft in a particularly smooth manner.
In a further development of the invention, it is provided that the swivelling lever is provided with a working surface situated outside the sleeve for a control element which disengages the sleeve. It is therefore possible, for example, in the event of a yarn breakage, to automatically stop the feeding bottom roller although the drive shaft continues to rotate. In this case, the working surface must be arranged such that the control element acts against the direction of the spring force.
Advantageously, the sleeve is disposed on the drive shaft by means of slide bearings. This results in a particularly narrow construction in the radial direction. In this case, it is expedient for the sleeve to be secured in the axial direction on the drive shaft by means of an elastic ring.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.